Agricultural balers gather, compress, and shape crop material into a bale. There are different types of balers which create rectangular or square bales or cylindrical or round bales. Bales can be bound with netting, strapping, wire, or twine. A baler that produces small rectangular bales is often referred to as a square baler. Another type of baler is one that produces large rectangular bales, often referred to as large square baler.
Large square balers have been used in crop harvesting for many years. One advantage over other types of balers is that they densify the crop into large rectangular shaped bales, which can minimize shipping and storage costs. Large square balers usually utilize a compression system including a gearbox with a fixed length crank arm and a fixed length connecting rod which is attached to a plunger. During each rotation of the crank arm, the plunger compresses the crop in a baling chamber by extruding the crop though a rectangular chute as the plunger moves towards the rear of the baler. Crop is usually metered from a pre-compression chamber into the baler chamber. One purpose for having a pre-compression chamber is to collect enough crop material to make a full flake of hay prior to moving the crop in front of the plunger to be compressed.
One of the problems with balers having a fixed length connecting rod is that the plunger movement and speed cannot be varied relative to the crank arm speed. For a given crank arm speed, the plunger compresses the crop at the same speed for each stroke, and the dwell time of the plunger at the extended position is also the same for each stroke.